Curtain coating machines



March '7, 1967 $0 W ET AL 3,367,518

' CURTAIN COATING MACHINES 2 Sheets-Sheet 1 Filed Dec. 15, 1965INVENTORS v $00M Y, Wo/vc;

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CURTAIN COATING MACHINES Filed Dec. 13, 1963 2 Sheets-Sheet 2 INVENTORSSooy y. Wow; Tao W5 A. 6020) AND BY [FM/7N Pau'rz/We-e United StatesPatent 3,307,516 CURTAIN COATING MACHINES Soon Y. Wong and Travis L.Gordy, Ponca City, Okla., and Irwin Politziner, Brigham City, Utah,assignors to Continental Oil Company, Ponca City, Okla., a corporationof Delaware Filed Dec. 13, 1963, Ser. No. 330,447 4 Claims. (Cl.118-324) such as the Steinemann curtain coater, the basic elements ofthe machine comprise a coating head through which is passed a thin filmof a liquid coating composition, which film is allowed to gravitate fromthe head in a substantially vertical plane so as to form a curtainusually having a width of several feet. The falling coating compositionis collected in a trough spaced vertically downwardly from the coatinghead at which the curtain originates, and is then recirculated from thetrough to the head after being passed throughsuitable heating andde-gassing equipment.

Disposed in a common, substantially horizontal plane which extendsnormal to the falling curtain of the coating composition are a pair ofconveyors which serve to feed the stock to be coated through thecurtain. In the conventional curtain coating apparatus, the feedconveyor is a broad, belt-type conveyor which terminates adjacent thecurtain and feeds the flat stock into the curtain in such manner thatthe curtain strikes the upper surface of the stock at substantially aright angle. The discharge conveyor which removes the stock from thecurtain also terminates in close proximity to the curtain so that theleading edge of the stock is received by the discharge conveyor, and byfrictional engagement, the stock is moved out of the curtain and ontothe discharge conveyor for transfer to a point of disposition. The gapwhich exists between the feed and discharge conveyors, and through whichthe falling curtain passes, is directly above the trough and is oflesser width than the length of the stock which is to be coated.

In the case of thin, relatively small stocks which are to be coated inthe conventional curtain coating machines heretofore utilized, a problemhas existed in applying a uniform, blister-free coating to the stock asthe stock is passed through the falling curtain. This problem arisesfrom the fast that the dimensions of the stock only permit the stock tobarely bridge the .gap between the intake and discharge conveyors, andthe weight of the unsupported span of the stock, in addition to theimpact of the falling curtain on the upper surface of the stock resultsin a distortion or deflection of the stock from a single plane as itpasses through the curtain and over the collecting trough. This bendingmotion of the stock causes defects in the form of blisters and openspots to occur in the applied coating. The result of these defects isthat many of the cartons formed from the stock must be discarded and,for some combinations of coating materials and substrate stocks, thediscards reach such a high percentage as to make the curtain coatingoperation uneco'nomical.

The present invention provides an improvement in curtain coatingmachines which enables small, relatively thin stocks to be coated insuch machines with a smooth 3,307,516 Patented Mar. 7, 1967 coating ofuniform thickness, which coating is free of blisters and open, uncoatedspots. In one of its broader aspects, the invention comprises a grate ofnovel construction which is placed in the trough directly beneath thecoating head, and which provides a supporting platform for supportingthe stock as it passes through the gravitating curtain. In providingsuch support, the grate prevents the undesired deflection of the stockhereinbefore described, and thereby eliminates the development ofdefects in the coatings which require discard of the stock and cartonsmade therefrom.

The novel grating and curtain coating apparatus which includes suchgrating in combination therewith which are contemplated by the presentinvention may assume several forms, but in each embodiment, severalcommon features of the grating are perceptible, and are of substantialimportance to the effective functioning of the grating in the attainmentof the described ends. First of all, the grating does not present anysubstantial or considerable obstacle to the free passage of the coatingcomposition through the gap between the conveyors and into the troughbelow. It is important that the free circulation of the coatingcomposition be uninhibited except for such portion of the composition asis deposited upon the upper surface of the stock which is passed throughthe gravitating curtain.

A second important consideration in the novel grate construction is thatthe coating material does not collect in excessive amounts, or adherefor excessive periods of time, on the portion of the grate which iscontacted by the stock as it passes thereover. This is an importantfeature of the invention since otherwise such accumulated coatingmaterial will be deposited on the bottom side of the stock as it passesover the grate, thus marring this side of the stock. Such deposition ofthe coated composition is undesirable in every instance, and isparticularly undesirable when the bottom or second side of the stockmust subsequently be coated in another operation.

A final important feature of the novel grate of the pres ent inventionis that it affords a minimum of resistance to the free passage thereoverof the stock to be coated, and does not provide any abrupt edges orpoints upon which the stock may become impaled or scratched. In each ofthe embodiments of the invention, this is accomplished by the provisionof a minimum grate surface area in contact with the underside of thestock passing thereover, and a proper inclination or curvature of thegrate elements to assure that the stock moves easily onto the grate anddoes not become pierced through, or hung upon some portion of the grate.

From the foregoing general description and summary of the invention, itwill be perceived that the present invention provides a valuableimprovement in curtain coating machines of the type in which agravitating curtain of the coating composition to be used falls from acoating head to a receiving trough through a gap defined betweenconveyors used to feed stock into and through the gravitating curtain ofthe coating material. The invention permits several important objectivesto be achieved which have not heretofore been attainable in conventionalcurtain coating machines, one of the more important of which is ageneral improvement in the coating which is applied to the surface ofstock passed through the curtain coat-' ing apparatus.

A more specific object of the present invention is to provide animproved curtain coating apparatus in which fibrous stocks of relativelysmall area and thickness may be coated with more uniform and defect-freecoatings.

Another object of the invention is to reduce the percentage of coatedstock materials which must be discarded after coating such stocks usinga curtain coating machine of the type hereinbefore described.

A further object of the present invention is to provide an improvementin curtain coating machines of the type heretofore employed whichpermits the general appearance of fibrous stocks coated by the use ofthe machine to be improved and also improves the overall coating ratewhich can be attained when using such machines.

An additional object of the invention is to provide an improvement toconventional curtain coating machines, which improvement is readilyadaptable to the existing components of such machines, and isinexpensive to construct, install on the machines, and maintain.

In addition 'to the foregoing described objects and advantages,additional merits and useful aspects of the present invention willbecome apparent to the reader as the following detailed description ofthe invention is read in conjunction with a perusal of the accompanyingdrawings which illustrate the invention.

In the drawings:

FIGURE 1 is a schematic isometric view of one embodiment of theinvention which may be utilized for improving the coating applied tosmall, relatively thin stocks utilizing a curtain coating machine.

FIGURE 2 is a modified embodiment of the novel grating which is employedin combination with the conventional elements of a curtain coatingmachine in substantially the same manner illustrated in FIGURE 1.

FIGURE 3 is an isometric view of a third embodiment of the novel gratewhich may be used in the combination.

Referring now to the drawings in detail, and particularly, to FIGURE 1,a curtain coating machine is schematically illustrated and includes theconventional coating head 10, at which originates the gravitatingcurtain of'the coating composition, and the trough 12 which receives thecomposition and permits it to be recirculated to the head via a conduit14 by means of a suitable pump 16. The gravitating curtain of thecoating composition is represented in phantom by the dashed lines and isdesignated by reference character 18. Spaced above the trough 12 andoccupying substantially the same horizontal plane are a pair ofconveyors designated by reference characters 20 and 22. The conveyor 20may be termed the input or feed conveyor, and in one suitable form maycomprise a wide belt which passes around a roller 24 positioned adjacentthe gravitating curtain 18 and slightly to one side thereof. Theconveyor 22 may be designated a discharge conveyor and also comprises awide belt which passes around a roller 26 positioned adjacent thegravitating curtain 18 and on the opposite side thereof from the roller24. The conveyors 20 and 22 are aligned so that fibrous sheet stock 28may be moved into the curtain 18 on the feed conveyor 20 and picked upby the discharge conveyor 22 and moved to a disposal location.

It will be apparent in referring to FIGURE 1 that a gap is necessarilyprovided between the feed and discharge conveyors, 20 and 22,respectively, through which the gravitating curtain 18 of the coatingcomposition may pass. This gap is necessarily of a lesser width than thedimension of the sheet stock 28 measured along the line of its travel.Thus, in the course of its travel, the stock 28 forms a bridge acrossthe gap between the conveyors 20 and 22 and is at this time subjected tothe impingement of the falling coating material. As hereinbeforeexplained, when the stock is of relatively small areal size and isrelatively thin, the stock is deflected or bent from its monoplanarconfiguration so that the coating is not laid down on the upper surfacethereof in a uniform manner and defects in the nature of pinholes andblisters are formed in such coating. It is to the end of remedying thisdifficulty that the novel grates of the present invention areincorporated in the curtain coating apparatus in combination with theelements hereinbefore described.

In referring to FIGURE 1, the preferred embodiment of the grate of theinvention there illustrated comprises a pair of downwardly dependinglegs 30 positioned at each end of the trough 12, the legs in the twopairs being retained in the relative spacing with respect to each otheras shown in FIGURE 1 by a pair of elongated, horizontal connectingmembers 32 and a series of wire support members designated generally byreference character 34. The wire support members 34 include a pluralityof horizontally spaced, substantially parallel wires 36 which have theirupper surfaces positioned in substantially the same horizontal plane asthat occupied by the upper surface of the conveyors 20 and 22, and whichare each provided at their ends adjacent the feed conveyor 20 with adown turned toe portion 38. The wire support members 34 each furtherincludes a pair of wire posts 39 which extend vertically upward from theelongated connecting members 32 and interconnect the wires 36 with theconnecting members 32.

The legs 30, connecting members 32 and wire posts 39 of the gratestructure illustrated in FIGURE 1 are dimensioned to assure thepositioning of the wires 36 in the plane of travel of the lower surfaceof the stock 28 as it moves through the gravitating curtain of coatingmaterial. The Wires 36 are each fine and of relatively small diameter,and may conveniently be constructed, for example, of steel piano wire.We have found a 14-gauge piano wire to be useful for most applications.The horizontal distance which is provided between the several wires 36is governed by the size of the object to be coated, and the down turnedtoes 38 which are provided on the wires 36 adjacent the feedconveyor 20assure that the stock to be coated will not be caught or impaled on thewires. With the aid of the grate structure illustrated in FIGURE 1,stock employed for fabricating milk and butter cartons has beensuccessfully coated with hot melt coating compositions comprising blendsof a thermoplastic copolymer and wax. The coatings applied were of highquality and free of blisters and pinholes. Moreover, the grate did notimpart any undesirable deposition of the coating material to theunderside of the stock passed thereover.

In addition to the grate embodiment illustrated in FIG- URE 1 of thedrawings, two other embodiments have been successfully utilized in thecurtain coating apparatus. The first of these embodiments is illustratedin FIGURE 2 ofthe drawings. The embodiment of FIGURE 2 comprises twopairs of vertically extending, horizontally spaced legs 30 which areinterconnected by elongated connecting members 32. The wire supportmembers 34 used in the embodiment illustrated in FIGURE 1 are replacedby horizontally extending, parallel metallic bars 40 which are taperedat their upper edge to a knife edge 42. The knife edges'42 of the bars40 occupy the horizontal plane common to the upper surfaces of theconveyors 2i) and 22 so thatthe stock is moved smoothly across the bars40 in traversing the gap between the conveyors 20 and 22 in passingthrough the curtain 18. order toprevent grooving of the carton stock orimpalement on the bars 40, thecorners 44 of the bars adjacent the feedconveyor 20 are radiused so that the leading edge of the stock slipseasily onto the knife edge 42 of the bars without undue resistance.

The grate illustrated in FIGURE 2 of the drawings is positioned in thetrough 12 in substantially the same manner as is illustrated in FIGURE 1with the lower ends of the legs 30 resting on the bottom of the trough,and

.the stock supporting portion of the grate positioned in the gap betweenthe conveyors 20 and 22.

The third grate embodimentwhich may be used in the combination isillustrated in FIGURE 3 of the drawings. This embodiment comprises two.pairs of vertically extending legs 30 for supporting the grate in thetrough 12 in the manner hereinbefore described. Each of the pairs oflegs 30 is retained in its spatial relationship by a horizontal crossmember 48. Interconnecting the horizontal cross members 48 are aplurality of elongated parallel, connecting members 50 which extendnormal to the path of travelof the stock and are each provided with aplurality of upwardly extending spikes 52 which terminate at their freeupper ends in points. The points of the spikes 52 are all positioned ina common plane which corresponds to the plane of movement of the stock28. The spikes 52 are preferably inclined slightly with respect to thevertical and in a direction of inclination away from the input conveyor20. This inclination of the spikes 52 eliminates a tendency of the stockto catch on the spikes as the stock moves across and is supported by thespikes. The spacing of the rows of spikes 52 with respect to each otherand with respect to the feed conveyor 20 is of considerable importancerelative to the effectiveness with which the grate embodimentillustrated in FIGURE 3 may be used in combination with the otherelements of the curtain coating apparatus. Thus, each of the rows ofspikes must not be spaced from the next adjacent row of spikes nor mustthe first row of spikes be spaced from the feed conveyor 20 by adistance sulficient to permit the leading edge of the stock 28 to dipslightly and therefore abut against the sides of the spikes 52 prior tomoving smoothly onto the points of the spikes.

From the foregoing description of the invention, it is believed that theoperation and function of the invention will have become clearlyunderstandable. To summarize, however, in the operation of the curtaincoating apparatus including the improvement of the present invention,relatively thin stock of small areal size is moved toward thegravitating curtain of coating material upon the feed conveyor 20. As itreaches the gap between the feed conveyor 20 and the discharge conveyor32, the leading edge of the stock projects into the gap between theconveyors and Will move outwardly upon one of the grate structureshereinbefore described. In each of the grate embodiments, the supportingsurface which is provided for the stock as it moves across the gap andthrough the gravitating curtain 18 is of relatively small area, beingeither a point contact support as in the case of the embodimentillustrated in FIGURE 3 or essentially a linetype support as in the caseof the wire support members 34 in the FIGURE 1 embodiment of the grateor the knife edge structure shown in the FIGURE 2 embodiment. In thisWay, a minimum of resistance is afforded to the movement of the stock 28across the gap between the conveyors, and also the supporting structuredoes not present a large surf-ace upon which undesirable coatingmaterial accumulations may occur. The latter aspect of the gratestructure in turn avoids the possibility of transfer of coating materialto the under surface of the stock as it passes across the supportingstructure.

Although the present invention has been described with a certain degreeof particularity and detail, it is to be understood that certain minorchanges and modifications may be made in the structure described by wayof example in the foregoing specification without departure from thebasic principles underlying the invention. Changes of this type aretherefore intended to be considered Within the spirit and scope of theinvention except as the same may be necessarily limited by the appendedclaims or reasonable equivalents thereof.

We claim:

1. In a curtain coating machine of the type used to apply a thin uniformcoating to flat stock, the combination which comprises:

(a) a coating head for developing a gravitating curtain of the coatingcomposition;

(b) a trough positioned below the coating head for receiving the coatingcomposition;

(c) a pair of conveyors positioned on opposite sides of the gravitatingcurtain for moving the flat stock through the gravitating curtain in aplane extending through the curtain between the coating head and thetrough; and

(d) a grate positioned in the trough and providing a perforatesupporting surface in coplanar alignment with the plane of movement ofthe flat stock through the gravitating curtain for supporting the stockas it moves through said gravitating curtain, said grate comprising:

(1) a substructure resting in said trough, said substructure comprising:

(a) a pair of vertically extended rigid legs at each end of said trough;and (b) horizontal connecting members interconnected with the legs ofsaid pairs and maintaining the spacing of said legs from each other; and(2) a plurality of stock-supporting elements secured to said horizontalconnecting members and projecting upwardly therefrom, saidstocksupporting elements each terminating at its upper extremity in theplane occupied by the lower surface of said stock as it moves throughsaid curtain.

2. The combination claimed in claim 1 wherein said stock supportingelements comprise a plurality of parallel, elongated wires eachextending in the direction of travel of the stock through said curtain.

3. The combination claimed in claim 2 wherein each of said elongatedwires terminates at its end adjacent the conveyor moving the stock intosaid curtain in a downwardly turned toe portion.

4. The combination claimed in claim 1 wherein said stock supportingelements comprise a plurality of parallel, elongated bars each extendingin the direction of travel of the stock through said curtain, said barseach tapering to a knife edge at its upper edge with said knife edgesextending in substantially the same plane as the plane occupied by thelower surface of said stock as said stock moves through said curtain.

References Cited by the Examiner UNITED STATES PATENTS 237,836 2/1881Dupuy 118-501 X 1,093,245 4/ 1914 Best 99-446 1,146,845 7/1915 Burham34-239 1,976,066 10/ 1934 Friend 118-501 1,979,758 11/1934 Merritt118-324 2,101,161 12/1937 Whiteman 34-239 2,197,178 4/1940 Gates 34-239X 2,651,289 9/ 1953 Kitterman 118-324 3,204,753 9/1965 Mosely 198-1023,205,089 9/ 1965 Kinzelrnan 118-324 3,245,380 4/ 1966 Carroll 118-324FOREIGN PATENTS 364,197 10/ 1962 Switzerland.

DANIEL BLUM, Primary Examiner.

1. IN A CURTAIN COATING MACHINE OF THE TYPE USED TO APPLY A THIN UNIFORMCOATING TO FLAT STOCK, THE COMBINATION WHICH COMPRISES: (A) A COATINGHEAD FOR DEVELOPING A GRAVITATING CURTAIN OF THE COATING COMPOSITION;(B) A TROUGH POSITIONED BELOW THE COATING HEAD FOR RECEIVING THE COATINGCOMPOSITION; (C) A PAIR OF CONVEYORS POSITIONED ON OPPOSITE SIDES OF THEGRAVITATING CURTAIN FOR MOVING THE FLAT STOCK THROUGH THE GRAVITATINGCURTAIN IN A PLANE EXTENDING THROUGH THE CURTAIN BETWEEN THE COATINGHEAD AND THE TROUGH; AND (D) A GRATE POSITIONED IN THE TROUGH ANDPROVIDING A PERFORATE SUPPORTING SURFACE IN COPLANAR ALIGNMENT WITH THEPLANE OF MOVEMENT OF THE FLAT STOCK THROUGH THE GRAVITATING CURTAIN FORSUPPORTING THE STOCK AS IT MOVES THROUGH SAID GRAVITATING CURTAIN, SAIDGRATE COMPRISING: (1) A SUBSTRUCTURE RESTING IN SAID TROUGH, SAIDSUBSTRUCTURE COMPRISING: (A) A PAIR OF VERTICALLY EXTENDED RIGID LEGS ATEACH END OF SAID TROUGH; AND (B) HORIZONTAL CONNECTING MEMBERSINTERCONNECTED WITH THE LEGS OF SAID PAIRS AND MAINTAINING THE SPACINGOF SAID LEGS FROM EACH OTHER; AND (2) A PLURALITY OF STOCK-SUPPORTINGELEMENTS SECURED TO SAID HORIZONTAL CONNECTING MEMBERS AND PROJECTINGUPWARDLY THEREFROM, SAID STOCKSUPPORTING ELEMENTS EACH TERMINATING ATITS UPPER EXTREMITY IN THE PLANE OCCUPIED BY THE LOWER SURFACE OF SAIDSTOCK AS IT MOVES THROUGH SAID CURTAIN.